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THE AMERICAN NATURALIST [Vol. LIV 



results from both groups, it was found that the 131 individuals 

 with recognizable ovary or testis comprised 76 females and 55 

 males, 3 the females, when mature, being distinguishable exter- 

 nally by the development of a salmon-pink or orange-red colora- 

 tion of the soft parts (foot, head, ctenidia, mantle). 4 



3. The color difference between the sexes of Chiton is believed 

 to be of special significance, for the following reasons: because 

 the coloration of the soft parts of the female is directly traceable 

 to metabolic activities associated with the growth of the ovary; 

 and because it provides an example of secondary sexual colora- 

 tion which has no conceivable utility, but is, on the contrary, so 

 far«as color is concerned, of a thoroughly accidental nature. 



Concerning the first point: the data previously summarized 

 show the definite manner in which reddish pigmentation is cor- 

 related with sex; there are also the facts, (1) that in animals 

 less than 3.4 cm. length there is no trace of any pink body pig- 

 mentation, (2) that the intensity of such pigmentation agrees 

 with the state of development of the ovary, (3) that the blood 

 of female chitons is mahogany-red or deep orange in color (that 

 of males being dull yellow), and (4) that the reddish hue of 

 blood, external tissues, and ovary is demonstrably due to the 

 same pigment substance. 



This pigment shows by its chemical behavior that it belongs 

 to the group of carotin-like "lipochromes," and is unrelated to 

 the haemoglobin which colors the buccal musculature of both 

 sexes. It has also an absorption spectrum — one band in the 

 blue-green, another in the violet — of a kind supposed to be 

 characteristic of the "lipochromes." The pigment is not soluble 

 in water, but is dissolved by either 95 per cent, alcohol, acetone, 

 xylol, or chloroform, and by the last named is extracted from 

 alcohol after treatment with alkalies; it is quickly decolorized 

 by standing in contact with air, in the light, and is bleached 

 (after passing through a deep blue condition) to lemon yellow 

 by strong nitric acid. Concentrated solutions are orange-red, 



3 These figures give a sex ratio of males: females:: 1: 1.38; this is prob- 

 ably too high a proportion of females for the whole population, but there 

 seems undoubtedly to be, in some places, a preponderance of females. The 



